The present invention relates to certain novel composite materials and products made therefrom.
The composites and products of the invention are preferably prepared using the disclosure and teachings of my copending U.S. application Ser. No. 08/236,258, the entire contents of which are incorporated herein by reference. Said application makes reference to an article by Chou et al. entitled "Composites" appearing in Scientific American, October, 1986, Volume 255, No. 4, pages 192-203. This article, which includes an extensive discussion regarding composites comprising fibrous materials dispersed in various matrix materials, is also incorporated herein by reference. This article has a tacit assumption, consistent with industry thrust for some decades that designers/engineers of composites strive for high fiber-matrix bond levels. Ser. No. 08/236,258 teaches benefit from weak bond levels, soft, pliant, flexible resilient composites.
In Ser. No. 08/236,258, I have disclosed a composite material which comprises a polyurethane matrix reinforced with a fibrous material, e.g. one or more plies of fabric with a polyurethane matrix polymerized in situ, which is made by wetting the fibrous material with liquid polyurethane-forming reactants and allowing these to react at a temperature below the melting point of the fibrous material. The reaction results in the formation of a solid polymeric matrix as cure takes place. The rate of cure can be either accelerated by catalysts and heat or retarded by adding other chemicals or evacuating heat.
The present invention contemplates certain modifications in the product and process of Ser. No. 236,258 to enable the production of composite articles having a variety of properties as desired, for example, improved toughness, and the facility of producing three-dimensional products, cosmetic permanence, control of flexibility, control of grip, visual texture and barrier properties. Typical products contemplated by the invention include such varied articles as shoe outsoles, suitcases, furniture components, hoses, ducts, luggage, flags, awnings, the soft parts of umbrellas, decorated narrow tapes/straps, labels, helmets, seating, gloves, footwear, small boats, protective apparel and resilient floor and wall coverings or the like where such property combinations as flexibility, toughness, cosmetic variations and permanence, and breathability/fluid barriers are desired.
Broadly described, a product according to the invention comprises:
(1) a composite as in, for example, Ser. No. 08/236,258, comprising a solid polyurethane matrix surrounding a fibrous reinforcing material where the matrix is formed in situ by reaction of liquid matrix-forming materials about the fibrous material; and PA1 (2) a thermoplastic polymer film or the equivalent on one or both sides of the composite (1), the film being bound to the composite by adhesion to the polyurethane matrix, the adhesion being the result of physical and/or chemical reaction which occurs or is enhanced as the liquid matrix material cures to form the solid matrix.
The present products can be prepared in a variety of ways, for example, by placing one or more layers of the fibrous material on a flat or curved surface, over a male mold or across the cavity of a female mold or between the parts of a mating mold, wetting the layer(s) with a mixture of the polyurethane-forming reactants, placing the thermoplastic polymer film or its equivalent on the wetted layer(s) before any significant reaction occurs, causing the plies of the resulting layup to consolidate as desired and to take the shape of the mold as and when necessary and allowing the polyurethane-forming reaction to take place. This yields a flat or molded product with the polymer film adhesively bound to the polyurethane matrix.
The process as described above can be varied in numerous ways. For example, the layer(s) of fibrous material can be laminated to polymeric film prior to placing a layup containing such laminate on a mold or wetting it with the metered and mixed liquid parts from which a solid matrix will form in place on at least one surface of the film as well as on, around and among the fibers of the fibrous material.
The layers or plies of fibrous material may be wet while they are in place on a solid base or mold. Alternatively, they may be wet out before placing them on a base or mold, such as by passing them through a nip with the metered and mixed coreactive parts present.
Wet and dry plies of fibrous material may be used in the same layup, with the dry plies becoming partially or thoroughly wet out by virtue of contact with wet plies and consolidation of the plies.
It is also possible to prepare a product comprising multiple alternate layers of the reinforced matrix and polymer film by building up a repeated series of wetted layers of fibrous material followed by polymer film, wetted layers, polymer film and so on to the desired thickness level provided successive plies are consolidated suitably before any significant polyurethane formation occurs.
The fibrous material is preferably in the form of a knitted, stitch-bonded, woven, braided or non-woven fabric although fibers, filaments or yarns per se may also be used. Fabrics are, however, preferred as these facilitate wetting out and laying up of plies of fibers with the urethane-forming reactants prior to their positioning adjacent to one or more films. Typically, a plurality of fabric layers or plies are brought together, these plies are wet with the reactants, the polymer film is placed against the wetted plies and the process repeated as many times as desired before the polyurethane reaction is significantly underway.
The fibrous material may be of any available or engineered configuration or composition provided it has a melting point above the temperature of the polyurethane reaction. Typically, for example, the fibrous material comprises polyester, polyethylene, polypropylene, polyaramid, and/or like materials which do not harbor significant moisture but do have a significant quantity of reactive sites for the urethane-forming reactants. Mineral (typically with a bond promoter such as silane), animal, vegetable (including man-made cellulosics), nylon, acrylic, and like fibrous materials may be used in certain circumstances where higher levels of fiber-matrix bonding are desirable or where a cure is aided by moisture, such as a moisture-curing urethane.
The thermoplastic polymer film may also be of any desired composition, e.g. polyester, polyvinyl chloride or floride, polycarbonate, nylon, or polyurethane. Particularly desirable results are obtained when using polyurethane film having OH groups that can react with the polyurethane matrix parts as the matrix is being formed to provide improved bonding. Polyurethane films, typically thermoplastic polyurethane films, are available for use with such desirable properties as toughness, elasticity, clarity (including clarity after stretch or stretch/recovery), colorability (including good resolution of print thereon), barrier properties (permeability or resistance to passage of various categories of fluids), light stability, and chemical reactivity. The films which are used may be colored, printed, clear, smooth, textured, or perforated/pin-holed films. The thickness of such films can be widely varied and will depend on the product desired. A typical example is polyurethane film of two mils to 100 mils thickness, although it will be appreciated that other types of films and thickness can be used.
As indicated, the film may be clear (transparent) or it may be colored or carry a design, printing, texture, embossing, topography or the like on its surface. In one embodiment of the invention, a fabric layer within the matrix may be provided with a color, print or design so that if the polyurethane matrix and polymer film are transparent, the color, print or design will show through while being protected by the polymer film from wear, abrasion, sunlight or the like.
In another embodiment, the film itself may carry color, printing or a design either on an exposed surface or on an interior surface adjacent to the matrix in which case the film itself serves to protect the color, print or design.
Flexible or rigid molds, e.g. a vacuum bag against or over a rigid mold, may be used to shape the products of the invention as the polyurethane matrix is being formed in situ. Additionally, a release film may be used to facilitate release of the cured product from the base of mold. The release film may be elastic if needed to conform to a desired topography or to, for example, a 3-D mold, or it may be dimensionally stable, smooth surfaced or textured to suit. The release film may also be employed to influence shape or to impart a particular texture to the product or to emboss the same. This release film is then removed after the matrix has been partly or wholly cured.
A fabric material may also be used in lieu of, or together with, a release film to provide a desired outer surface. This may be accomplished by laying the fabric onto the fibrous material which has been wetted with the reactant mixture forming the polyurethane matrix. In this embodiment, the fabric material should be placed on the wetted fibrous material before the polyurethane-forming reaction has taken place to any substantial extent. The fabric may be used to mold the surface of the product or it may itself become an integral part of the product. If the fabric is to be used to mold or emboss the product, it should be selected so as to be non-reactive with the urethane-forming reactants to facilitate its release. On the other hand, if the fabric is intended to serve as a permanent part, of the surface of the product, it should preferably be chosen to react with or mechanically bond to the urethane forming reactants and to provide other desired surface features, e.g. to allow or prevent complete or partial strikethrough of the polyurethane resin as may be desired.
The fabric when used as described in the preceding paragraph, may vary greatly with respect to its composition and/or construction. Fabrics comprised of synthetic fibers such as polyester, polyethylene, polyaramid, polypropylene or like fibers which tend to be hydrophobic are preferred. However, in the case of certain moisture-cure urethanes, hydrophilic fibers may be of advantage.
The fabrics used for this embodiment may be woven, non-woven, knit, braided, stitch-bonded or combinations thereof, optionally replaced by or employed with laid yarns or filaments or random cut or continuous fibers.
Various alternatives are contemplated for making the products of the invention. For example, if desired, a vacuum bag, platen, belt or nip pressure may be employed during the forming of the composite. These techniques may be used, for example, to provide the desired consolidation, surface texture or topography to the composite. A preferred embodiment is to employ one film that serves as all or part of a vacuum bag as a product is being formed. After that film has been bound to the matrix, it becomes a permanent layer of that product.
Typically, when a plastic vacuum bag is used, either it is a release material itself or a release material is typically placed between the plastic vacuum bag containing the wetted fibrous layer or layers and the fabric and/or film placed thereon. Vacuum is applied as the polyurethane matrix is formed. The interior surface of the bag is drawn by the vacuum down against the release layer which in turn presses against the reinforcing or surfacing fabric or barrier film as the polyurethane matrix is formed.
In a further feature of the invention, the present products may be cut, vertically or at any other desired angle, so that the fiber ends of the fibrous reinforcement within the matrix are exposed. This can be done to provide a surface of increased wear resistance for products made therefrom or for cosmetic or other reasons. According to this embodiment, a single layer of polyurethane matrix with fiber reinforcement, but, preferably, multiple layers of the same and separated or covered by polymeric film, may be rolled up, with or without using a mandrel, to form a cylindrically shaped composite product. This can then be cut in a direction transverse to the longitudinal axis to provide a disc or washerlike composite product comprising the matrix with ends of the reinforcing fibers exposed. This method may be used to prepare brake facings, outsoles, top lifts or the like where wear resistant surfaces are required. The product to be cut, according to this embodiment, may be formed directly on a mandrel by co-winding one or more wet fabric plies on the mandrel, with one or more polymer films on and/or between fabric plies and curing the windup to form the polyurethane matrix in situ. If multiple polymeric-film plies are employed, typically one has been perforated.
Alternatively, the product to be cut may be wound up while wet without a mandrel for subsequent curing and cutting.
Rather than roll up the product on itself or on a mandrel, the product, whether single ply or multiple alternate plies of similar or dissimilar materials, may simply be cut at the appropriate angle to expose the fiber ends. The angle may be perpendicular to the axis of any reinforcing/wear surface fiber, although other cutting angles are desirable in certain cases, to provide a particular grip/slip or cosmetic effect.
The polyurethane-forming reactants used in Ser. No. 08/236,258 may be used for present purposes. These reactants are particularly useful as they permit ready wetting of the fibrous reinforcement material while the reactants have a low molecular weight and particle size is small so that mobility of the reactants is high, facilitating wet out of the surfaces of the fibrous component. Furthermore, their reaction rates can be controlled to permit the required laying up and consolidating of a desired number of layers before significant reaction occurs. This also facilitates forming the product before the matrix changes to the solid state thus avoiding permanent stress on the matrix or reinforcing fibers as a consequence of molding after the matrix is a solid.
Typically, the polyurethane-forming reactants comprise (A) an aliphatic or aromatic isocyanate, e.g. an isocyanate monomer such as isophrone diisocyanate or diphenylmethane diisocyanate and (B) a hydroxy component such as a polyether or polyester polyol or a mixture thereof with other chemicals such as polypropylene glycol. Any conventional polyurethane-forming components may be used for this purpose provided the polyurethane reaction occurs at a temperature below the melting point of the fibrous component. Preferably, the polyurethane is formed by separately preheating the reactants (A) and (B) to a temperature of, for example, 30.degree.-80.degree. C., metering and mixing the reactants together and applying the reactant mixture about the fibrous component by, for example, spraying, troweling, or between nip rolls, the fibrous component or components being held in a mold or otherwise supported at ambient (18.degree. C.-32.degree. C.) or elevated temperature (up to the melt point of the fibrous component) while wet out of the fibrous component becomes thorough. The subsequent in situ reaction is an exothermic one which can be controlled, if necessary, to keep the temperature well below the melting point of the fibers involved. Heat to accelerate a cure can be beneficial. Usually, the temperature will be kept below about 70.degree. C. although higher temperatures, e.g. up to about 120.degree. C., may be used with certain fibrous materials.
As an example of one specific embodiment of the invention, several plies of non-woven fabric composed of high tenacity polyethylene fibers are placed on top of each other and wetted with the polyurethane-forming reactants. A six-mil thermoplastic clear aliphatic barrier polyurethane film is placed on an exterior surface of the wetted-fabric layup. Consolidation is aided by vacuum. The polyurethane-forming reaction is then allowed to proceed in generally the manner described in Ser. No. 08/236,258 so as to form a polyurethane matrix around the polyethylene fibers with the polyurethane film bound thereto. The resulting composite may be about 0.01 to 10 inches thick although other thicknesses may be effectively employed.
The polyurethane film used in the above example can be selected to provide a product with a variety of surface characteristics. For example, the film may be receptive to ink and thus provide means for coloring or printing on the surface. Film with a planar surface suitable for high-resolution printing or another surface or coloring means for excellent color depth may be selected. The polyurethane barrier layer is advantageously applied by vacuum processing as all or part of a vacuum bag or in a plastic bag or the equivalent so that air pockets affecting color or performance of the product are removed as the polyurethane matrix is being formed in situ. This may be done by putting a release sheet which is textured on one or both sides, and a vacuum bag on one or both sides, of the layup as the polyurethane matrix formation is taking place. This must be done before the polyurethane matrix is in the solid state, preferably while the reactant parts are liquid and mobile. Adhesion is obtained between the film and the fiber-reinforced matrix of the composite. Without intending to be limited to this explanation, a chemical reaction occurs between the polyurethane film, which bears reactive OH groups, and NCO groups present in one of the matrix reactants in excess of the 1:1 ratio of NCO required to mate with OH in the other matrix reactant. Usually a reactant NCO:OH ratio of 1.05:1 to 1.15:1 is appropriate to provide the required matrix-forming reaction and leave some NCO for reaction with OH in the film material. The film is thus adhered chemically to the matrix although mechanical adhesion is also possible. Such mechanical adhesion can be controlled by consolidation of the liquid polyurethane-forming reactants into and around surface irregularities or engineered receiving shapes or holes in the fibers or films present, and effecting cure while consolidation conditions endure.
It is possible to provide printing on either side of the thermoplastic polyurethane film if desired. It is also possible to tint or intensively color the film throughout. The matrix may also be tinted or intensively colored before it cures and, albeit not preferable, after it cures. It is also possible to color or print some or all the reinforcing fabrics before the matrix is put in place. An advantage of doing this is that the color of the reinforcing fabric will not migrate subsequent to curing of the matrix, the color being shielded from UV rays, abrasion, and similar hazards by the urethane matrix which by itself can be clear, allowing the use of printing materials and techniques that might be otherwise unqualified because of marking off or the like.
In another embodiment of the invention, the fibrous component may be replaced in whole or in part or supplemented by the addition of particulate reinforcement or filler or colorant material. This may include, for example, metal, plastic or rubber particles, minerals or inorganic filler materials, or organic pigments. Other examples of such particulate reinforcing materials include silicon carbide, silica, carbon black, zinc oxide, titanium dioxide, organic pigments or microspheres.